1. Field of the Invention
This invention relates to packaging apparatus and to methods carried out by such apparatus. More particularly, this invention relates to methods and apparatus for making evacuated, hermetically-sealed packages from plastic film, and for making such packages containing an inert gas such as nitrogen.
2. Description of the Prior Art
It is well known in the prior art to make hermetically-sealed packages from plastic film. Such packages typically may be evacuated prior to sealing, for example, to increase the shelf life of food products. For certain types of products, it also has been found desirable to introduce an inert gas into the package before sealing.
Various types of automatic packaging machines designed to make hermetically-sealed packages have been available for a number of years. Reference may be made in that regard to U.S. Pat. Nos. 3,061,984 and 3,524,298. Although such machines have been quite satisfactory for most packaging applications, problems have occurred when using conventional machines for packaging products of the type with top layers comprising liquid or semi-liquid materials, i.e. products having portions which are relatively non-cohesive. For example, when the product consists of a portion of solid food material covered with a topping consisting of a layer of liquid or semi-liquid sauce, sprinkled with a ground condiment, it has been found that in conventional machines the rapid flow of air and gas during evacuation and/or gas-filling tends to shift and disarrange the topping of the product. Such disarrangement of the product destroys its aesthetic appearance, making it unattractive to prospective customers. Moreover, rapid flow of air and/or gas across the product can drive the liquid or semi-liquid product material out of the container receptacle and onto the flange sealing surfaces around the mouth of the receptacle, thereby interfering with the efficacy of the seal and resulting in leaky packages.
Such problems can of course be minimized simply by reducing the rate of flow of air or gas, but that in turn undesirably restricts the rate of package production.